Clays and oxide minerals as catalysts and nanocatalysts in Fentonlike reactions

Xúc tác clay và khoáng oxit trong phản ứng kiểu FentonClays and oxide minerals as catalysts and nanocatalysts in fenton like reactions Năm 1894 trong tạp chí hội hóa học Mỹ đã công bố công trình nghiên cứu của tác giả J.H Fenton trong đó ông quan sát thấy phản ứng oxy hóa axit malic bằng muối được sử dụng làm tác nhân oxy hóa rất hiệu quả cho nhiều đối tượng rộng rãi các chất hữu cơ và được mang tên là “ tác nhân Fenton”.

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Review Article

Clays and oxide minerals as catalysts and nanocatalysts in Fenton-like

E.G Garrido-Ramíreza, B.K.G Thengb,⁎ , M.L Morac

a

Programa de Doctorado en Ciencias de Recursos Naturales Universidad de La Frontera, Av Francisco Salazar 01145, Casilla 54-D, Temuco, Chile

bLandcare Research, Private Bag 11052, Palmerston North 4442, New Zealand

c

Scientiﬁc and Technological Bioresources Nucleus, Departamento de Ciencias Químicas, Universidad de La Frontera, Av Francisco Salazar 01145, Casilla 54-D, Temuco, Chile

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 5 May 2009

Received in revised form 20 November 2009

Accepted 21 November 2009

Available online 29 November 2009

Keywords:

Allophane

Catalysts

Clays

Fenton-like reaction

Oxide minerals

Zeolites

Advanced oxidation processes (AOP), involving the generation of highly oxidizing radical species, have attracted much attention because of their potential in eliminating recalcitrant organic pollutants from different environmental matrices Among the most investigated AOP is the Fenton reaction in which hydroxyl radicals (HOU) are generated through the catalytic reaction of Fe(II)/Fe(III) in the presence of

hydrogen peroxide The use of clays and iron-oxide minerals as catalysts of Fenton-like reactions is a promising alternative for the decontamination of soils, groundwaters, sediments, and industrial efﬂuents The low cost, abundance, and environmentally friendly nature of clay minerals and iron oxides are an added advantage Additionally, the introduction of nanoparticles in heterogeneous catalytic processes has led to appreciable improvements in catalytic efﬁciency Here we review the application of clays and iron-oxide minerals as supports or active catalysts in Fenton-like reactions, and summarize the latest advances in nanocatalyst development We also evaluate the potential use of allophane nanoparticles, coated with iron oxides, as catalysts of Fenton-like reactions

1 Introduction

The development of processes, such as advanced oxidation, for the

ef ﬁcient degradation of persistent organic pollutants in the

environ-ment has attracted a great deal of interest Advanced oxidation

processes involve the generation of reactive radicals, notably hydroxyl

radicals (HO U ) that are highly oxidative and capable of decomposing a

wide range and variety of organic compounds ( Ramírez et al., 2007a ).

Depending on the structure of the organic compound in question,

different reactions may occur including hydrogen atom abstraction,

electrophilic addition, electronic transfer, and radical –radical

inter-actions ( Nogueira et al., 2007 ).

Advanced oxidation processes (AOP) use a combination of strong

oxidants such as ozone, oxygen, or hydrogen peroxide and catalysts

(e.g., transition metals, iron), semiconductor solids together with

sources of radiation or ultrasound ( Primo et al., 2008a ) Typical AOP

include O3/UV, H2O2/UV, TiO2/UV, H2O2/O3 ( Pérez-Estrada et al.,

Initially developed by Fenton (1894) for the oxidation of tartaric acid,

this reaction has been used for the decomposition and removal of

hydrocarbons ( Kong et al., 1998; Kanel et al., 2004; Ferrarese et al.,

2008 ), organic dyes ( Núñez et al., 2007; Cheng et al., 2008 ), antibiotics

Sulzberger, 1999; Gallard and De Laat, 2000; Saltmiras and Lemley, 2002; Ventura et al., 2002; Chan and Chu, 2005; Barreiro et al., 2007;

phenols ( Barrault et al., 1998; Farjerwerg et al., 2000; Barrault et al., 2000b; Catrinescu et al., 2003; Carriazo et al., 2005b; Araña et al.,

decontam-ination ( Rincón and Pulgarin, 2007; Shah et al., 2007 ).

The Fenton process involves the reaction of Fe(II) with hydrogen peroxide, giving rise to hydroxyl radicals as shown in Eq (1) This catalytic reaction is propagated by the reduction of Fe(III) to Fe(II) as shown in Eq (2) with the generation of more radicals as depicted by Eqs (3) –(5).

Fe2þþ H2O2→Fe3þþ OH−þ HO• Ea¼ 39:5 kJ mol−1 k1¼ 76 M−1s−1

ð1Þ

Fe3þþ H2O2→Fe2þþ HO•2þ Hþ Ea¼ 126 kJ mol−1 k2¼ 0:001–0:01 M−1s−1

ð2Þ

Fe2þþ HO•2→Fe3þþ HO−2 Ea¼ 42 kJ mol−1 k3¼ 1:3 106M−1s−1

ð3Þ

⁎ Corresponding author Tel.: +64 6 353 4945; fax: +64 6 353 4801

E-mail address:thengb@landcareresearch.co.nz(B.K.G Theng)

Contents lists available at ScienceDirect

Applied Clay Science

j o u r n a l h o m e p a g e : w w w e l s ev i e r c o m / l o c a t e / c l ay

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Fe3þþ HO•2→Fe2þþ O2þ Hþ Ea¼ 33 kJ mol−1 k4¼ 1:2 106M−1s−1

ð4Þ

H2O2þ HO•→HO•2þ H2O Ea¼ 14 kJ mol−1 k5¼ 2:7 107M−1s−1:

ð5Þ Typical values of the activation energy (Ea), and apparent rate

constant (k) for these reactions are taken from Lee and Yoon (2004)

The generation of hydroxyl radicals in the Fenton reaction has

been used in a variety of processes: (1) homogeneous Fenton process,

involving iron(II) salts dissolved in an acid medium, (2),

heteroge-neous catalysis ( ‘Fenton-like reaction’), (3) photo-reduction of Fe(III)

to Fe(II) through the use of ultraviolet radiation ( ‘photo-Fenton

process ’) ( Zeep et al., 1992; Feng et al.;, 2003a,b, 2004c, 2009; Farré

et al., 2007; Malato et al., 2007; Schwingel de Oliveira et al., 2007;

The homogeneous Fenton process has been widely investigated

2005; Barros et al., 2006; Deng and Englehardt, 2006; Deng, 2007; Li

et al., 2007; Nogueira et al., 2007; Núñez et al., 2007; Schwingel de

simple process uses a conventional equipment and operates at

ambient temperatures and pressures The process, however, has

some drawbacks due mainly to the formation of different Fe(III)

complexes as solution pH changes.

The optimum pH for the homogeneous Fenton process is about 2.8

when the iron in solution occurs partly as Fe(III) and partly as Fe(III)

(OH)2+, representing the photo-active species Below this pH, the

hydroxyl radicals are scavenged by protons and the concentration of

Fe(III)(OH)2+declines while above this pH, Fe(III) precipitates as an

oxyhydroxide ( Pignatello, 1992; Sum et al., 2005; Li et al., 2007;

of ∼3, large amounts of acid (usually sulphuric acid) must be added

to the reaction medium ( Valdés-Solís et al., 2007b ) Thus, it is

impractical to apply the homogeneous Fenton process to in situ

envi-ronmental remediation because (without pH adjustment) large

amounts of ferric hydroxide sludges would be produced, creating

disposal and other environmental problems ( Catrinescu et al., 2003;

On the other hand, heterogeneous solid catalysts can mediate

Fenton-like reactions over a wide range of pH values ( Caudo et al.,

catalysts is “immobilized” within the structure and in the pore/

interlayer space of the catalyst As a result, the catalyst can maintain

its ability to generate hydroxyl radicals from H2O2, and iron hydroxide

precipitation is prevented ( Catrinescu et al., 2003; Chen and Zhu,

catalysts can easily be recovered after the reaction, and remain active

during successive operations ( Centi et al., 2000; Sum et al., 2005;

A range of heterogeneous solid catalysts, including activated

carbon impregnated with iron and copper oxide metals have been

used to degrade recalcitrant organic compounds through the

Fenton-like reaction ( Georgi and Kopinke, 2005; Ramírez et al., 2007b ) Some

examples are Na fion film or Nafion ( Fernandez et al., 1998, 1999;

iron-coated pumice particles ( Kitis and Kaplan, 2007 ), and

iron-immobilized aluminates ( Muthuvel and Swaminathan, 2008 ).

Clays and oxide minerals, either as such or as supports of iron and

other metal species, can also serve as heterogeneous catalysts in the

Fenton-like reaction ( Halász et al., 1999; Barrault et al., 2000b; Chirchi

and Ghorbel, 2002; Carriazo et al., 2005b; Baldrian et al., 2006; Matta

et al., 2007; Bobu et al., 2008; Chen et al., 2008; Ortiz de la Plata et al.,

2008 ) Indeed, these materials provide an attractive alternative for the decontamination of soils, underground waters, sediments, and industrial ef ﬂuents because they are natural, abundant, inexpensive, and environmentally friendly ( Watts et al., 1994, 2002; Watts and Dilly, 1996; Andreozzi et al., 2002a; Carriazo et al., 2005b; Aravindhan

natural and synthetic zeolites exchanged with iron or copper ions

pillared interlayered clays ( Barrault et al., 1998; Guélou et al., 2003; Li

et al., 2006; Giordano et al., 2007; De León et al., 2008; Sanabria et al.,

2008 ) and iron-oxide minerals ( Lin and Gurol, 1998; Kwan and Voelker, 2002, 2003; Wu et al., 2006; Matta et al., 2007; Hanna et al.,

However, these catalysts, especially those containing iron(III) oxides, need ultraviolet radiation to accelerate the reduction of Fe(III)

to Fe(II) This is because the reaction, depicted in Eq (2), is much slower than the decomposition of H2O2 in the presence of Fe(II) (Eq (1)) as used in the photo-Fenton process ( Kwan and Voelker,

process is generally more ef ﬁcient than its normal (non-irradiated) Fenton or Fenton-like counterpart but the operating cost of the former

is quite high in terms of energy and UV-lamp consumption ( Centi

whole catalyst be accessible to light.

nanosize particles with a high surface area that can accelerate the Fenton-like reaction without requiring UV radiation These nanoca-talysts are very reactive because the active sites are located on the surface As such, they have a low diffusional resistance, and are easily accessible, to the substrate molecules Nanocatalysis is but one of the many practical applications of nanotechnology which is concerned with the synthesis and functions of materials at the nanoscale range ( b100 nm) ( Mamalis, 2007; Miyazaki and Islam, 2007; Lines, 2008 ).

An important feature of nanomaterials is that their surface properties can be very different from those shown by their macroscopic or bulk counterparts ( Theng and Yuan, 2008 ) As the term suggests,

‘nanocatalysis’ uses nanoparticles and nanosize porous supports with controlled shapes and sizes ( Bell, 2003 ).

This review describes the use of clays and iron-oxide minerals as supports or active catalysts in the Fenton-like reaction, and sum-marizes recent advances in the development of nanocatalysts with improved catalytic ef ﬁciency We also evaluate the potential of allophane nanoparticles, coated with iron oxides, to serve as catalysts

in the Fenton-like reaction.

2 Heterogeneous solid catalysts

A wide range of solid materials, such as transition metal-exchanged zeolites ( Pulgarin et al., 1995; Farjerwerg and

copper species ( Barrault et al., 1998; Guélou et al., 2003; Li et al., 2006;

iron-oxide minerals ( Lin and Gurol, 1998; Kwan and Voelker, 2002, 2003; Wu et al., 2006; Matta et al., 2007; Hanna et al., 2008; Liou and

oxidative degradation of organic compounds through the Fenton-like reaction By combining the ef ﬁciency of the homogeneous Fenton process with the advantages of heterogeneous catalysis, these materials show great promise for the treatment of highly recalcitrant organic pollutants.

Solid catalysts must ful ﬁll a number of requirements, such as high activity in terms of pollutant removal, marginal leaching of active

183 E.G Garrido-Ramírez et al / Applied Clay Science 47 (2010) 182–192

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cations, stability over a wide range of pH and temperature, and a high

hydrogen peroxide conversion with minimum decomposition (

also be available at a reasonable cost.

2.1 Transition metal-exchanged zeolites

Zeolites are hydrated aluminosilicates with a cage-like structure.

Their internal and external surface areas may extend to several

hundred square meters per gram, while their cation exchange

capacities are up to several milliequivalents per kilogram At least

41 types of natural zeolites have been identi ﬁed, and many others

have been synthesized Zeolites have an open porous structure

capable of accommodating a wide variety of exchangeable cations,

including iron ( Ku šić et al., 2006; Tekbas et al., 2008 ).

Zeolites are ideal catalysts because the dimension of their pores is

similar to that of the reacting molecules ( Neamtu et al., 2004b;

function as both selective adsorbents and ‘in situ’ oxidation catalysts

zeolites can vary according to the experimental conditions as do their

macroscopic properties ( Ovejero et al., 2001b; Neamtu et al., 2004b;

pore structure, transition metals (e.g., iron, copper) are not prone to

leach out or precipitate during the process ( Neamtu et al., 2004b ).

Zeolites containing transition metal ions have been shown to be

ef ﬁcient catalysts in the oxidation of a range of organic pollutants

through the Fenton-like reaction ( Ovejero et al., 2001b; Doocey et al.,

photo-Fenton process ( Rios-Enriquez et al., 2004; Noorjahan et al., 2005;

Kasiri et al., 2008; Muthuvel and Swaminathan, 2008; Tekbas et al.,

2008 ), and the wet oxidation process using hydrogen peroxide

degrade organic pollutants through the Fenton reaction (Eq (1)) by

generating HO U radicals that can diffuse into the bulk solution This

implies that the pollutants are decomposed in the external medium as

well as within the zeolite framework Ku šić et al (2006) have

pro-posed a similar mechanism for the degradation of phenol by Fe-ZSM-5

zeolite, while Noorjahan et al (2005) concluded that the enhanced

activity of a Fe(III)-HY zeolite system was due to the synergistic effect

of pollutant adsorption and HO U radical diffusion.

In common with the homogeneous Fenton process, the ef ﬁciency

of heterogeneous Fenton-like catalysis is in ﬂuenced by several

operating parameters, such as iron concentration, type of iron catalyst,

H2O2concentration, iron catalyst/hydrogen peroxide ratio,

tempera-ture, pH and treatment time ( Doocey et al., 2004; Ku šić et al , 2006 ).

Data on the degradation of recalcitrant organic compounds through

the Fenton reaction, using Fe- and Cu-exchanged zeolites, are

summarized in Table 1

These studies show that the catalytic ef ﬁciency and stability

against leaching of Fe-exchanged zeolites are related to their iron

content For example, Doocey et al (2004) found that the rate of

hydrogen peroxide decomposition was higher for Fe-4A zeolite (3.4%

w/w iron) than Fe-Beta zeolite (1.25% w/w iron) At the same time,

the former was slightly more stable in the cation leaching test The

catalytic ef ﬁciency and stability of Fe-exchanged zeolites are also

affected by pH and temperature Using Fe-Beta and Fe-4A zeolites as

catalysts, Doocey et al (2004) observed optimal hydrogen peroxide

decomposition at pH 3.5 Neamtu et al (2004b) reported that the

degradation of the Azo dye Procion Marine H-EXL by Fe-Y zeolite was

higher at pH 3 (97%) than at pH 5 (53%) in 10 min of operation, while

increasing the time of operation to 30 min resulted in 97% removal at

pH 5 For the reaction at pH 3, this (initial) value did not change

throughout the treatment During the reaction at pH 5, however, the

pH decreased to about 3.5 This might be because the dye molecules fragment into organic acids as the reaction proceeds As a result, solution pH decreases and the degradation process is accelerated

zeolite Thus, Fe-exchanged zeolites can effectively operate at near neutral pH as cation leaching is limited, and zeolite stability is maintained ( Doocey et al., 2004; Neamtu et al., 2004a,b ).

Although a rise in temperature increases catalytic ef ﬁciency, it also enhances cation leaching and decomposition of hydrogen peroxide to oxygen and water Neamtu et al (2004a) found an optimal temperature of 50 °C for the degradation of the azo dye C.I Reactive Yellow 84 (RY84) by wet hydrogen peroxide oxidation using

a Fe-exchanged Y zeolite catalyst.

The preparation of metal-exchanged zeolites also in ﬂuences catalytic activity Valkaj et al (2007) , for example, reported that the activity of a Cu-ZSM-5 catalyst prepared by direct hydrothermal synthesis (DHS) was higher than that of a catalyst obtained by the ion exchange (IE) method in terms of phenol oxidation and hydrogen peroxide decomposition The stability of the DHS catalyst was also superior to that of the IE material because leaching of the active ingredient was relatively low in the former instance.

Using a Fe-exchanged zeolite, Centi et al (2000) compared the catalytic ef ﬁciency of the homogeneous Fenton process with that of the (heterogeneous) Fenton-like reaction The Fe-ZSM-5 catalyst was more ef ﬁcient in degrading propionic acid (72%) than the homoge-neous Fenton process (43%) The heterogehomoge-neous process was also less sensitive to changes in pH.

2.2 Pillared interlayered clays Pillared interlayered clays (PILC) are low-cost, microporous solid catalysts with unique properties and structures ( Li et al., 2006;

metal polycations into swelling clay minerals, notably smectites On heating at high temperatures ( ≈500 °C), the intercalated polycations are converted into the corresponding metal oxide clusters through dehydration and dehydroxylation By propping the silicate layers apart, these oxides act as “pillars”, creating interlayer meso- and micro-pores ( Mishra et al., 1996; Kloprogge, 1998; Bergaya et al.,

oxocations increases the basal spacing of the parent clays The increase in basal spacing is higher for Fe-supported Al-PILC catalysts (Fe –Al-PILC) than for their Fe-PILC counterparts Li et al (2006)

reported a basal spacing increment of 0.62 nm for Fe –Al-PILC and 0.51 nm for Fe-PILC with respect to the original bentonite clay, while

Al –Fe-PILC, while Pan et al (2008) observed an increment of 0.64 nm for Al-PILC prepared from Na-montmorillonite.

The surface area of PILC, determined by adsorption of N2gas at

77 K and applying the Brunauer –Emmett–Teller (BET) equation, is invariably much larger than the corresponding starting clay or clay mineral For example, Pan et al (2008) measured a surface area of

176 m2g− 1 for Al-PILC as against 43 m2g− 1 for the original Na-montmorillonite Similarly, Li et al (2006) obtained a BET surface area

of 114.6 m2g− 1 for Fe-PILC and 194.2 m2g− 1 for Al –Fe-PILC as compared with 31.8 m2g− 1 for the original bentonite clay In addition, pillaring greatly increases the accessibility of interlayer catalytic sites to the reactant molecules ( Kloprogge, 1998; Carriazo

Pillared interlayered clays containing oxocations of copper (Cu-PILC) or iron (Fe-(Cu-PILC) together with Al-PILC supporting iron and copper ions, have been widely used as catalysts for the degradation of recalcitrant organic compounds via Fenton-like reactions,

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photo-Fenton reactions, and wet hydrogen peroxide oxidation ( Table 2 ).

Pillared interlayered clay catalysts are also very stable, showing

minimal leaching of interlayer metal species to the external solution

Ramírez et al., 2007a; Bobu et al., 2008; Caudo et al., 2008; Pan et al.,

repeatedly with little loss of catalytic activity, while problems

associated with water contamination by soluble metals and waste

disposal are avoided The relatively short periods of operation are an added advantage of using PILCs catalysts.

In investigating the wet acid oxidation by H2O2of p-coumaric acid and p-hydroxybenzoic acid using Cu-PILC with different Cu loadings (0.5, 1.0 and 2.0% Cu), Caudo et al (2008) , for example, found that 76 – 82% of total organic carbon (TOC) was removed within 4 h of operation Similarly, Sanabria et al (2008) observed 100% removal

of phenol in 2 h of operation by a Fenton-like reaction, using Fe-PILC in

Table 1

Catalytic degradation of organic compounds over iron- or copper-exchanged zeolites through different Fenton-like processes

Compound Catalyst/support Process Reference

Remazol Brilliant Orange 3C Fe(III)-exchanged natural zeolite Photo-Fenton Tekbas et al (2008)

Indigoid dye C.I Acid Blue 74 Fe-ZSM-5 synthetic zeolite Photo-Fenton Kasiri et al (2008)

Reactive Brilliant Blue KN-R Fe-NaY and Fe-ZSM-5 Fenton-like reaction Chen et al (2008)

Azo dye Acid Violet 7 Fe(III) immobilized Al2O3catalyst Photo-Fenton Muthuvel and Swaminathan (2008)

Azo dye Porción Marine H-EXL Fe-exchanged Y zeolite Wet hydrogen peroxide oxidation Neamtu et al (2004b)

Acid brown Mn-exchanged Na-Y zeolite Wet hydrogen peroxide oxidation Aravindhan et al (2006)

C.I Reactive Yellow 84 (RY84) Fe-Y zeolite Wet hydrogen peroxide oxidation Neamtu et al (2004a)

Phenol Fe-ZSM-5 zeolite Wet hydrogen peroxide oxidation Huu Phu et al (2001)

Phenol model wastewater Fe-ZSM-5 Fenton-like reaction and Photo-Fenton Kušić et al (2006)

Phenol Cu-Y-5 Wet hydrogen peroxide oxidation Zrnčević and Gomzi (2005)

Chlorinated phenols Fe-Beta zeolite Fenton-like reaction Doocey et al (2004)

Fe-4A zeolite Phenolic solutions Fe-NaY, Fe-USY, and Fe-ZSM-5 Fenton-like reaction Ovejero et al (2001b)

Phenol Fe(III)-HY catalyst Photo-Fenton Noorjahan et al (2005)

Phenol MFI zeolite Wet hydrogen peroxide oxidation Ovejero et al (2001a)

Phenol Fe-ZSM-5 Wet hydrogen peroxide oxidation Farjerwerg et al (2000)

Phenolic aqueous wastes Fe-ZSM-5 Wet hydrogen peroxide oxidation Farjerwerg and Debellefontaine (1996)

Phenolic aqueous wastes Fe-ZSM-5 Wet hydrogen peroxide oxidation Farjerwerg et al (1997)

4-Nitrophenol Fe-ZSM-5 Photo-Fenton Pulgarin et al (1995)

Phenol Cu-ZSM-5 Wet hydrogen peroxide oxidation Valkaj et al (2007)

1,1-Dimethylhydrazine and ethanol Fe-MF1 zeolite catalyst Fenton-like reaction Kuznestsova et al (2008)

1,1-Dimethylhydrazine Fe-ZSM-5 zeolite Fenton-like reaction Makhotkina et al (2006)

Carboxylic acids Fe-ZSM-5 Wet hydrogen peroxide oxidation Centi et al (2000)

Acetic acid Cu–NaY zeolite Wet hydrogen peroxide oxidation Larachi et al (1998)

2,4-xylidine Fe(III)-zeolite Y Fenton-like reaction Rios-Enriquez et al (2004)

Table 2

Pillared interlayered clays (PILC) as heterogeneous catalysts for the decomposition of various organic compounds via Fenton-like reactions

Compound Catalyst/support Clay Process Reference

Azo dye X-3B Fe-PILC Bentonite Photo-Fenton Li et al (2006)

Al–Fe-PILC Methylene blue Fe-PILC Natural montmorillonite Photo-Fenton De León et al (2008)

Orange II Hydroxyl-Fe-PILC Bentonite Photo-Fenton Chen and Zhu (2006)

Acid Light Yellow G Fe-PILC (catalyst) Natural bentonite Photo-Fenton Chen and Zhu (2007)

Azo dye Orange II solution Al-PILC impregnated with Fe Natural saponite Fenton-like reaction Ramírez et al (2007a)

Ciproﬂoxacin (ﬂuoroquinolones) Fe-PILC Laponite (synthetic hectorite) Photo-Fenton Bobu et al (2008)

nanocomposite Phenol Mixed (Al–Fe)-PILC Commercial Greek bentonite Catalytic wet oxidation with H2O2 Barrault et al (2000a)

Phenol Al–Cu-PILC Commercial Greek bentonite Catalytic wet oxidation with H2O2 Barrault et al (2000b)

Al–Fe-PILC Phenol Al- or mixed

Al–Fe-complexes PILC

Commercial Greek bentonite Catalytic wet oxidation with H2O2 Guélou et al (2003)

Phenol Fe-PILC Laponite Photo-Fenton Iurascu et al (2009)

4-Nitrophenol Fe(III)-exchanged PILC Montmorillonite Fenton-like reaction Chirchi and Ghorbel (2002)

Phenol Al–Cu-, Al–Fe- and Fe-PILC Natural sodium bentonite and

natural sodium montmorillonite

Catalytic wet oxidation with H2O2 Carriazo et al (2003)

Phenol Fe-exchanged Synthetic beidellite Catalytic wet oxidation with H2O2 Catrinescu et al (2003)

Al-PILC Phenol Al-, Al–Fe- and Al–Ce–Fe-PILC Natural Colombian bentonite Catalytic wet oxidation with H2O2 Carriazo et al (2005a)

Phenol Al–Fe-PILC Natural Colombian bentonite Fenton-like reaction Carriazo et al (2005b)

Al–Ce–Fe-PILC Phenol Al–Fe-PILC Natural bentonite Catalytic wet oxidation with H2O2 Sanabria et al (2008)

Benzene Al-PILC as supports

for Cu, V, Fe

Natural sodium montmorillonite

Fenton-like reaction Pan et al (2008)

p-Coumaric acid and p-hydroxybenzoic

acid olive oil mill wastewater

Cu-PILC Commercial bentonite Catalytic wet oxidation with H2O2 Caudo et al (2007)

Fe-PILC Polyphenols olive oil mill wastewater Cu-based zeolite Zeolite and commercial bentonite Catalytic wet oxidation with H2O2 Giordano et al (2007)

Cu-PILC Wastewater from agro-food production Cu-PILC Commercial bentonite Catalytic wet oxidation with H2O2 Caudo et al (2008)

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an aqueous medium, while Giordano et al (2007) were able to

remove 97% of polyphenols from olive oil mill wastewater within 3 h,

using Cu-PILC in a wet oxidation process with H2O2 Although the

optimal pH for the Fenton and photo-Fenton processes is around 3

are active over a wide range of pH ( De León et al., 2008 ), and offer the

potential to operate at near neutral pH without signi ﬁcant loss of

activity ( Chen and Zhu, 2007; Bobu et al., 2008; Caudo et al., 2008 ).

As already remarked on, this is because the Fe(III) species is largely

“immobilized” in the interlayer space of the clay mineral As such, the

iron in PILC is stable against changes in solution pH and shows only

limited leaching Further, the strong surface acidity of some Fe-PILC

allows catalytic activity to be maintained over a wide range of pH

values ( Chen and Zhu, 2006, 2007; De León et al., 2008 ) In using

Fe-PILC as heterogeneous catalysts, H2O2is often added to the solution at

near neutral pH As the reaction proceeds, however, the solution pH

decreases due to the formation of acidic intermediates (e.g., acetic

acid, oxalic acid) These acids can capture any Fe ions that are released

from the catalyst, giving rise to soluble complexes and promoting a

homogeneous Fenton process The concentration of Fe in solution is

proportional to that of the pollutant When the acidic intermediates

are mineralized (oxidized) to CO2and H2O, the Fe ions can be

re-adsorbed to the PILC surface, forming an Fe(III) cycle ( Bobu et al., 2008 ).

2.3 Iron-oxide minerals

The ability and potential of iron-oxide minerals to catalyze the

oxidation of organic compounds through the Fenton-like reaction

have been well documented ( Lin and Gurol, 1998; Huang et al., 2001;

Kwan and Voelker, 2002, 2003; Baldrian et al., 2006; Wu et al., 2006;

Matta et al., 2007; Hanna et al., 2008; Liou and Lu, 2008; Ortiz de la

investi-gated include goethite ( Kong et al., 1998; Lin and Gurol, 1998; Huang

et al., 2001; Kwan and Voelker, 2003; Wu et al., 2006; Liou and Lu,

2008 ), hematite ( Huang et al., 2001; Matta et al., 2007 ), magnetite

lepidocrocite ( Matta et al., 2007 ).

Iron oxides, used for wastewater decontamination, can be

recovered and reused because they are practically insoluble in

water Since iron minerals are widespread in the soil environment,

they can also be used for the in situ remediation of soils and

groundwaters through the Fenton-like reaction in the presence of

does not require strict control of pH as is the case in the homogeneous

Fenton process ( Andreozzi et al., 2002a ) Several authors, for example

have reported that the iron/hydrogen peroxide system can catalyze

the oxidation of pollutants at pH values between 3 and 7 through a

Fenton-like reaction ( Table 3 ) The process apparently involves

hydroxyl radicals, generated by decomposition of hydrogen peroxide

on the surface of iron-oxide particles through a chain reaction

mechanism ( Lin and Gurol, 1998; Huang et al., 2001; Kwan and

the oxidation of organic compounds can occur through a non-radical

mechanism ( Table 4 ).

According to the radical mechanism proposed by Lin and Gurol

complex between hydrogen peroxide (H2O2) and ≡Fe(III)–OH groups

at the oxide surface ( Table 4 , Eq (2.1) ) The surface complex may be

regarded as a ground-state (Eq (2.2) (mediating a reversible

elec-tronic transfer from ligand to metal The elecelec-tronically excited state

can be deactivated through dissociation of the peroxide radical

( “successor complex”), as shown by Eq (2.3) Being very active, the

peroxide radical can immediately react with other compounds.

Therefore, the reverse reaction of Eq (2.3) may be assumed to be

negligible (K NNK ) The reduced iron can react with either hydrogen

peroxide or oxygen, as shown by reactions 2.4 and 2.4a Reaction 2.4a , however, is slower than reaction 2.4 The hydrogen and peroxide radicals produced can react with Fe(II) and Fe(III), exposed on surface sites, according to reactions 2.6 and 2.7 These free radicals can also react with H2O2(reactions 2.8 and 2.9 ) Finally, the radicals can react with themselves, terminating the reactions ( 2.10 and 2.11 ).

On the other hand, Andreozzi et al (2002a) have suggested a non-radical mechanism for the degradation of 3,4-dihydroxybenzoic acid

as shown by Eqs (2.22) and (2.23) ( Table 4 ) where (*) denotes the active sites on the catalyst and CIis their concentration (mol dm− 3) The adsorbed substrate (S) and hydrogen peroxide react on the catalyst surface, giving rise to reaction products and the regeneration

of active sites (Eq (2.24) ).

The ef ﬁciency of iron-oxide minerals in catalyzing the decompo-sition of the organic pollutants through the Fenton-like reaction is

in ﬂuenced by several parameters, such as hydrogen peroxide con-centration, type and surface area of the iron mineral, solution pH (and ionic strength), and pollutant characteristics ( Matta et al., 2007; Yeh

determining the rate of formation of hydroxyl radicals (VOH▪) in iron oxide/hydrogen peroxide systems VOH▪is proportional to the product

of the concentrations of surface area of the iron oxide and hydrogen peroxide, with a different coef ﬁcient of proportionality for each iron oxide.

Since the concentration of hydrogen peroxide is directly related

to the amount of hydroxyl radicals produced in the catalytic reaction, this parameter in ﬂuences degradation efﬁciency In investigating the oxidation of dimethyl sulphoxide (DMSO) by hydrogen peroxide with goethite as catalyst, Wu et al (2006) found that when the

H2O2concentration was increased from 2.5 to 10 g/L, more hydroxyl radicals were generated, and the rate of degradation increased However, when the dosage of H2O2was further increased from 10 to

15 g/L, the rate of decomposition declined This was ascribed to scavenging of H2O2by hydroxyl radicals resulting in the formation of hydroperoxide radicals that were much less active and did not con-tribute to the oxidation of DMSO.

As regards mineral type, Fe(III) oxides are catalytically less active than their Fe(II) counterparts ( Kwan and Voelker, 2003 ) In evaluating the activity of different iron minerals in catalyzing the degradation of 2,4,6-trinitrotoluene (TNT) through a Fenton-like reaction in aqueous solution at pH 3, Matta et al (2007) found that iron(III) oxides (hematite, goethite, lepidocrocite, and ferrihydrite) were less effec-tive than Fe(II) minerals, such as magnetite and pyrite.

The surface area of iron-oxide minerals is also an important factor

in ﬂuencing the degradation of organic pollutants by the Fenton-like reaction Hanna et al (2008) , for example, observed that the ef ﬁciency

of four quartz –iron-oxide mixtures in degrading methyl red (MR) at

pH 5 decreased in the order quartz –goethite (Q4) Nquartz/amorphous iron(III) oxide (Q1) Nquartz–maghemite (Q2) Nquartz–magnetite (Q3) This was also the order by which the surface area of the mineral mix-tures decreased: Q4(148 m2g−1) NQ1(121 m2g−1) NQ2(11.5 m2g−1) N

Q3(8.6 m2g−1).

Other factors in ﬂuencing the degradation of organic compounds

by iron oxides are medium pH and chemical properties of the pollutant At acid pH values, the degradation process is mainly due to dissolution of iron oxides in solution, promoting the homogeneous Fenton-like reaction Liou and Lu (2008) studied the degradation of explosives (2,4,6-trinitrophenol and ammonium picrate) by hydrogen peroxide at pH 2.8, using goethite as catalyst Here again, the under-lying mechanism involves dissolution of goethite and the generation

of ferrous ions which react with H2O2to produce HO U , according to the

homogeneous Fenton process In studying the oxidation of atrazine using ferrihydrite as catalyst, Barreiro et al (2007) found that the rate

of oxidation strongly depended on pH A high degradation rate was observed at pH 3 –4 when ferrihydrite dissolution strongly increased The increase in oxidation rate at low pH was attributed to the

Trang 6

enhanced solubility of iron (III) species at acid pH, promoting the

homogeneous Fenton reaction Fe(III) can also be solubilized by

forming complexes with organic acid intermediates produced during

pollutant degradation ( Feng et al., 2006; Martínez et al., 2007; Bobu

At near neutral pH values, the solubility of iron-oxide minerals

decreases, and hence the degradation of organic compounds (on the

catalyst surface) is mediated by the heterogeneous Fenton reaction

which controls the ef ﬁciency of the process Under these conditions,

the electrostatic interactions between the catalyst surface and the

organic compounds become important Kwan and Voelker (2004)

investigated the effect of electrostatic interaction between catalyst (goethite) surface and several probe molecules (formic acid, nitro-benzene and 2-chlorophenol) on their oxidization by H2O2 At pH 4, formic acid was negatively charged and interacted with the positively charged iron-oxide surface where HO U species were generated As a result, the oxidation rate of formic acid increased by a factor of 50 relative to that of the neutral molecule This observation provides strong support for the hypothesis that surface-adsorbed organic compounds are readily accessible to oxidation by HO U radicals.

oxide-quartz mixtures in degrading methyl red (MR) at pH 5 and 7 The high catalytic activity at pH 5 was ascribed to electrostatic interactions between the carboxylate group of MR (pKa = 5.1) and the partially protonated oxide surface (PZC N6) Since the soluble iron concentration at both pH values was below the limit of detection, adsorption of MR to the solid oxide surface had a determining in ﬂuence

on the degradation of MR through the heterogeneous Fenton reac-tion Wu et al (2006) found that the goethite-catalyzed degradation of dimethyl sulphoxide (DMSO) decreased in the order: pH 5 NpH 3NpH

7 ≈pH 10 They suggested that electrostatic interactions between the partial negative charge on the oxygen atom of DMSO and the partially protonated goethite surface at pH 5 favoured degradation.

2.4 Nanocatalysts

An important feature of nanoparticles is that their surface properties can deviate markedly from those of their macroscopic (bulk) counter-parts ( Theng and Yuan, 2008 ) In terms of catalysis, the activity and selectivity of nanocatalysts are strongly dependent on their size, shape, and surface structure, as well as on their bulk composition ( Bell, 2003;

nanoparticulate catalysts have been described by Bell (2003), Perez (2007), Bach et al (2008), and Dhakshinamoorthy and Pitchumani

recalcitrant organic compounds are given in Table 5 Liu (2006) have proposed that nanoparticles are potentially useful for remediating polluted sites because they can reach or penetrate into zones that are inaccessible to microsize solid catalysts.

The application of nanoparticles as catalysts of the Fenton-like and photo-Fenton reactions has been described by several investigators

nanoparticles show a higher catalytic activity because of their large

Table 3

Oxidation of various organic compounds catalyzed by iron-oxide minerals through Fenton-like processes

Bromophenol Blue, Chicago Sky Blue, Cu

Phthalocyanine, Eosin Yellowish, Evans

Blue, Naphthol Blue Black, Phenol Red,

Poly B-411, Reactive Orange 16

Magnetic mixed iron oxides (MO–Fe2O3); M = Fe, Co, Cu, Mn

Fenton-like reaction Baldrian et al (2006)

Methyl red (MR) Quartz/amorphous iron(III) oxide,

quartz/maghemite, quartz/magnetite, and quartz/goethite

Fenton-like reaction Hanna et al (2008)

2,4,6-Trinitrophenol and ammonium picrate Goethite Fenton-like reaction Liou and Lu (2008)

2,4,6-Trinitrotoluene Ferrihydrite, hematite, goethite,

lepidocrocite, magnetite and pyrite

Fenton-like reaction Matta et al (2007)

2-Chlorophenol Ferrihydrite, goethite and hematite Fenton-like reaction Huang et al (2001)

2-Chlorophenol Goethite Fenton-like reaction Lu et al (2002)

Benzoic acid [gamma]-FeOOH Fenton-like reaction Chou and Huang (1999)

3,4-Dihydroxybenzoic acid Goethite Hydrogen peroxide in aqueous slurry Andreozzi et al (2002a)

Petroleum-contaminated soils

(diesel and kerosene)

Goethite and magnetite Fenton-like reaction Kong et al (1998)

Aromatic hydrocarbons and chloroethylenes Goethite Fenton-like reaction Yeh et al (2008)

Atrazine Ferrihydrite Fenton-like reaction Barreiro et al (2007)

Aromatic substrates Goethite Hydrogen peroxide in aqueous slurry Andreozzi et al (2002b)

Dimethyl sulphoxide Goethite Fenton-like reaction (aqueous solution) Wu et al (2006)

Table 4

Mechanisms proposed for the oxidation of organic compounds on the surface of

iron-oxide catalysts through a Fenton-like reaction

1 Radical mechanism proposed byLin and Gurol (1998)

≡Fe(III)−OH+H2O2⇔(H2O2)s (2.1)

(H2O2)s⇔(≡Fe(II)⁎O2H) + H2O (2.2)

(≡Fe(II)⁎O2H)⇔Fe(II)+HO2⁎ (2.3)

≡FeðIIÞ + H2O2→K 4 ≡ FeðIIIÞ−OH +⁎OH + H2O (2.4)

FeðIIÞ + O2→K 4a FeðIIIÞ−OH + HO⁎

HO⁎⇔H2 ++ O2⁎−pKa = 4.8 (2.5)

≡FeðIIIÞ−OH + HO⁎

2= O⁎−

2 →K 6 ≡ FeðIIÞ + H2O= OH−+ O2 (2.6)

⁎OH +≡FeðIIÞ →K 7 ≡ FeðIIIÞ−OH (2.7)

⁎OH +ðH2O2Þs→K 8 FeðIIIÞ−OH + HO⁎

2+ H2O (2.8)

ðH2O2Þs+ HO⁎2= O⁎−

2 →K 9 ≡ FeðIIIÞ−OH + H2O= OH−+⁎OH + O2 (2.9)

HO⁎2+ HO⁎2→K 10 ðH2O2Þs+ O2 (2.10)

⁎OH + HO⁎

2= O⁎−

2 →K 11 H2O2+ O2 (2.11)

2 Radical mechanism proposed byKwan and Voelker (2003)

≡Fe(III)+H2O2→≡Fe(HO2)2+

+ H+

(2.12)

≡Fe(HO2)2+→≡Fe(II)+HO2⁎ (2.13)

≡Fe(II)+H2O2→Fe(III)+⁎OH+OH− (2.14)

⁎OH+H2O2→H2O + HO2⁎ (2.15)

≡Fe(II)+O2⁎−→≡Fe(III)+O2 (2.16)

≡Fe(III)+HO2⁎→≡Fe(II)+HO2 − (2.17)

≡Fe(II)+HO2 −→≡Fe(III)+HO2⁎ (2.18)

3 Non-radical mechanism proposed byAndreozzi et al (2002a)for the oxidation of

3,4-dihydroxybenzoic acid in a goethite/H2O2system

≡Fe(III)–OH (catalytically active sites on goethite) (2.19)

≡Fe(III)–OH+H+

→≡Fe(III)–OH2+ (2.20)

≡Fe(III)–OH→Fe(III)–O−+ H+

(2.21)

H2O2+ð⁎Þ ↔K h H2O⁎

2 Kh=½H2 O⁎2

H 2 O 2 C I

(2.22)

S +ð⁎Þ →K 1

S + H2O⁎

2→K 2 products + 2ð⁎Þ (2.24)

Trang 7

speci ﬁc surface where catalytically active sites are exposed ( Nurmi

Fenton-like reactions would more than offset the disadvantage

(associated with the use of iron(III) catalysts) of requiring ultraviolet

radiation to accelerate the reaction.

In investigating the catalytic degradation of ethylene glycol and

phenol by iron(III) oxide nanoparticles in the absence of ultraviolet

radiation, Zelmanov and Semiat (2008) found that the rate of

degradation was 2 –4 and 35 times higher, respectively, than the

values reported in the literature using Fenton's reagent/H2O2/UV.

oxidation of carbon monoxide and methane at low temperatures.

One of the materials (NANOCAT®) had an average particle size of

3 nm and a speci ﬁc surface area of 250 m2g− 1, while the other

material (Fe2O3PVS) had an average particle size of 300 nm and a

surface area of 4 m2g− 1 Although both catalysts were effective, the

nanocatalyst showed superior activity because of its high surface area.

Using a nanocasting technique, Valdés-Solís et al (2007b) obtained

MnFe2O4nanoparticles as heterogeneous catalysts for the Fenton-like

reaction These solid nanocatalysts were active over a wide range of

pH values (6 –13) and H2O2concentrations (0.005 –3 M).

3 Iron-oxide-coated allophane nanocatalysts in

Fenton-like reactions

Allophane is the main component of the clay fraction of soils

derived from volcanic ash and weathered pumice (Andisols) which

are widespread in southern Chile Iron oxides of short-range order,

notably ferrihydrite, are also widespread in Andisols although their

concentration rarely exceeds 10% ( Galindo, 1974 ) These constituents

often occur as coatings of clay mineral particles.

Allophane may be de ﬁned as “a group of clay-size minerals

with short-range order which contain silica, alumina, and water in

chemical combination ” ( Par ﬁtt, 1990 ) Allophanes occur as hollow

spherules with an external diameter between 3.5 and 5.5 nm and a

wall thickness of 0.7 –1.0 nm Defects in the wall structure give rise

to perforations of about 0.3 nm in diameter permitting water

mole-cules to enter the inner-spherule void ( Henmi and Wada, 1976; Wada

has distinguished three types of allophane with different structural

features: (a) Al-rich type, also referred to as ‘proto-imogolite’ or

‘imogolite-like’ allophane, with an Al/Si ratio of ∼2, (b) Si-rich type, sometimes referred to as ‘halloysite-like’ allophane, with an Al/Si ratio

of ∼1, and (c) stream-deposit allophane with Al/Si ratios ranging from 0.9 to 1.8 As the name suggests, type (c) allophane does not occur

in soil The speci ﬁc surface area of allophane, determined by adsorp-tion of polar liquids (ethylene glycol, ethylene glycol monoethyl ether), ranges from 300 to 600 m2g− 1, and from 145 to 170 m2g− 1 when measured by adsorption of nitrogen gas and applying the BET equation ( Díaz et al., 1990 ).

with a wide range of Al/Si ratios (0.19 –1.96) in order to assess the effect of composition on texture Transmission electron microscopy (TEM) shows differences in aggregate size and density Aggregates of allophanes with a relatively low Al/Si ratio are less dense than those with high Al/Si ratios, probably because the former samples have a low isoelectric point and surface charge The shape of the nitrogen adsorption –desorption isotherms also varies with Al/Si ratio Samples with an Al/Si ratio b0.5 have high adsorption volumes at P/Po∼1, suggesting the presence of relatively large mesopores and a wide pore-size distribution Samples with an Al/Si ratio of 0.5 –0.8 show marked hysteresis between the adsorption and desorption branches, indicative of a narrow pore-size distribution Samples with an Al/Si ratio of 0.8 –1.3 show high microporosity, low adsorbed nitrogen volume, and limited mesoporosity Samples with an Al/Si ratio N1.3 have a low nitrogen adsorption capacity.

aluminosilicates by both coprecipitation of sodium silicate and aluminium chloride and hydrolysis of tetraethylortosilicate and terbutoxyde of aluminium Besides being faster, the coprecipitation method gave materials with similar surface charge characteristics to those shown by natural allophanes Mora et al (1994) and Jara et al.

allophane-like materials which they then coated with iron oxides, using a wet impregnating technique They proposed that the iron oxide (coat) was attached to the allophane surface through Si –O–Fe and Al –O–Fe bonds.

The 57Fe Mössbauer spectrum at 300 K of iron-oxide-coated synthetic allophane, is shown in Fig 1 The presence of a broad paramagnetic doublet with a quadrupole splitting ( Δ) of 0.86 mm s−1, a line width ( γ) of 0.51 mm s−1, and an isomer shift ( δ) of 0.36 mm s−1is typical of high-spin ferric iron in octahedral coordination (to O and

OH ligands), corresponding to a ferrihydrite-like material ( Childs and

Table 5

Nanocatalysts used in the degradation of various organic compounds

Compound Nanocatalyst Process Reference

Orange II Composite of iron-oxide

and silicate nanoparticles

(Fe-nanocomposite)

Photo-Fenton reaction

Feng et al

(2003a)

Orange II Fe3+

-doped TiO2and bentonite clay-based

Fe nanocatalyst

Feng et al

(2004a)

Orange II Bentonite clay-based

Fe-nanocomposite

Feng et al

(2004b)

Trichloroethene Pd-on-Au Aqueous-phase

hydrodechlorination

Nutt et al

(2006)

Butachlor Immobilized TiO2

nanoparticles

Photocatalysis in aqueous solution

Mahmoodi

et al (2007)

Nonylphenyl poly

(oxyethylene)

ethers (NPE-10)

Au-doped nano-TiO2 Photo-degradation Du et al

(2008)

Orange G Iron–nickel bimetallic

nanoparticles

Degradation in aqueous solution

Bokare

et al (2008)

Phenol Chain-like Ru

nanoparticle arrays

Hydrogenation in aqueous media

Lu et al

(2008)

Lindane and

atrazine

Fe–Pd bimetallic

nanoparticles

Aerobic and anaerobic degradation

Joo and Zhao (2008)

Cango red Selenium

nanoparticles

Photocatalytic decolorization

Yang et al

(2008)

Fig 1.57

Fe Mössbauer spectrum (at 300 K) of synthetic allophane coated with iron

Trang 8

transmission electron micrographs of the same iron-oxide-coated

synthetic allophane Individual hollow allophane spherules with an

outer diameter of about 5 nm can be seen to form 30 –50 nm aggregates

that, in turn, coalesce into globular clusters, similar to what Hall et al.

of zero charge (PZC) of the samples was determined using the method

described by Parks (1967) , while the isoelectric point (IEP) was assessed

by electrophoretic mobility measurements The measured values of

∼4.2 for the PZC and ∼8.5 for the IEP, were consistent with the presence

of an iron-oxide coating over allophane-like particles, causing an overall

increase in surface acidity.

The nanosize clay fraction separated from an Andisol (Piedras

Negras series) in southern Chile, has an Al/Si ratio of 0.24 and a BET

nitrogen surface area of 124 m2g− 1(unpublished results) The shape

of the nitrogen adsorption –desorption curves of this natural nanoclay

was very similar to that reported by Montarges-Pelletier et al (2005)

for a synthetic allophane-like material with an Al/Si ratio b0.5,

indi-cating a high volume of mesopores, and a wide distribution of pore

sizes The nanoclay has a PZC of 3.8 and an IEP of 7.0 These values are

similar to those shown by an iron-oxide-coated allophane-like

material reported by Mora et al ( Mora, 1992; Mora et al., 1994; Jara

The potential use of allophane nanoparticles and allophanic soils

for pollution control has been described by several investigators ( Diez

et al., 1999, 2005; Vidal et al., 2001; Navia et al., 2003, 2005; Yuan and

deodorizer, humidity-controlling agent, membrane for separating

CO2, and support for enzyme immobilization ( Suzuki et al., 2000;

Little information, however, is available about the ability of iron-oxide-coated allophane nanoparticles to catalyze the decomposition

of organic compounds through Fenton-like reactions.

chlorophenols using electrodes of glassy carbon (GC) covered with synthetic iron-oxide-coated aluminosilicates (AlSiFe-GC) with three different Si/Al ratios and isoelectric points of 3.2, 7.2 and 8.2 The catalytic activity of all three AlSiFe-GC electrodes was similar, indicating that the basicity of AlSiFe did not affect the electro-oxidation process Subsequently, Pizarro et al (2005) evaluated the catalytic potential of iron oxides, separated from volcanic soils, using the gas-shift reaction of iron in water More recently, Cea (2006)

investigated the decomposition of pentachlorophenol (PCP), 2,4,6-trichlorophenol (2,4,6-TCF) and 2,4-dichlorophenol (2,4-DCF) cata-lyzed by the clay fraction of an Andisol under ultraviolet radiation The reaction followed ﬁrst-order kinetics, the rate of photolysis being dependent on the degree of chlorine substitution, and decreasing in the order: PCP N2,4,6-TCFN2,4-DCF.

The stability of iron-oxide-coated allophane as a heterogeneous catalyst in Fenton-like reactions has not been previously investigated Our research group has looked into the dissolution of synthetic allophane and its iron-oxide-coated counterpart between pH 4 and

pH 7 The preliminary data (unpublished) for synthetic allophane showed that 8.6 mg Al and 16 mg Si per gram allophane were dis-solved at pH 4.5 The corresponding values for iron-oxide-coated allophane were 1.2 mg Al/g and 3.3 mg Si/g Dissolution decreased dramatically ( b1 mg/g) at near neutral pH, and became negligible at

pH N7 Similarly, the stability of iron-rich minerals (as heterogeneous catalysts) is strongly dependent on solution pH As already men-tioned, the solubility of such minerals increases at low pH On other hand, the iron species incorporated into pillared interlayered clays (PILCs) is relatively resistant to (acid) leaching, and appears to be more stable than its counterpart in zeolites or oxide minerals This observation may be ascribed to strong binding (coordination) of the iron species to the interlayer surface of the clay mineral ( De León

the layer structure of clay minerals is more stable against leaching than exchangeable iron in the interlayer space ( Cheng et al., 2008 ).

4 Conclusions Clays and iron-oxide minerals possess structural and surface charge characteristics that are conducive to their use as supports

of catalytically active (Fe, Cu) phases, or as solid heterogeneous catalysts for the Fenton-like reaction These minerals can operate over

a wide range of pH and temperature, are easy to separate, and retain activity during successive treatments The catalytic ef ﬁciency of solid catalysts in decomposing organic pollutants through the hetero-geneous Fenton-like reaction is in ﬂuenced by the following fac-tors: concentration and type of catalyst, surface area of catalyst, hydrogen peroxide concentration, medium temperature, medium pH, and pollutant structure.

The use of nanocatalysts is a promising alternative to conventional catalysis Because of their large surface area and low diffusional resistance, nanoparticles are more ef ﬁcient than conventional heterogeneous catalysts The ability of nanocatalysts to operate in the absence of ultraviolet radiation is an added advantage Iron-oxide-coated allophane nanoparticles can catalyze the degradation of persistent organic pollutants through the Fenton-like reaction, and are useful for treating industrial ef ﬂuents The Fenton-like reaction may also be used for in situ remediation of contaminated soil, sediment, and groundwater because nanosize clays and iron oxides are ubiquitous in the natural environment.

Fig 2 Transmission electron micrographs of synthetic allophane Top (a): adapted from

Mora et al (1994); bottom (b): unpublished data

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Abidin, Z., Matsue, N., Henmi, T., 2007a Differential formation of allophane and imogolite:

experimental and molecular orbital study J Comput.-Aided Mater Des 14, 15–18

Abidin, Z., Matsue, N., Henmi, T., 2007b Nanometer-scale chemical modiﬁcation of

nano-ball allophane Clays Clay Miner 55, 443–449

Andrade, L.S., Ruotolo, L.A.M., Rocha-Filho, R.C., Bocchi, N., Biaggio, S.R., Iniesta, J.,

García-Garcia, V., Montiel, V., 2007 On the performance of Fe and Fe, F doped Ti–Pt/

PbO2electrodes in the electrooxidation of the Blue Reactive 19 dye in simulated

textile wastewater Chemosphere 66, 2035–2043

Andreozzi, R., Caprio, V., Marotta, R., 2002a Oxidation of 3, 4-dihydroxybenzoic acid by

means of hydrogen peroxide in aqueous goethite slurry Water Res 36, 2761–2768

Andreozzi, R., D'Apuzzo, A., Marotta, R., 2002b Oxidation of aromatic substrates in

water/goethite slurry by means of hydrogen peroxide Water Res 36, 4691–4698

Araña, J., Pulido, M.P., Rodríguez, L.V.M., Peña, A.A., Doña, R.J.M., González, D.O., Pérez,

P.J., 2007 Photocatalytyc degradation of phenol and phenolic compounds part I

Adsorption and FTIR study J Hazard Mater 146, 520–528

Aravindhan, R., Fathima, N.N., Rao, J.R., Nair, B.U., 2006 Wet oxidation of acid brown

dye by hydrogen peroxide using heterogeneous catalyst Mn-salen-Y zeolite: a

potential catalyst J Hazard Mater 138, 152–159

Arnold, S.M., Hickey, W.J., Harris, R.F., 1995 Degradation of atrazine by Fenton's

reagent: condition optimization and product quantiﬁcation Environ Sci Technol

29, 2083–2089

Bach, A., Zelmanov, G., Semiat, R., 2008 Cold catalytic recovery of loaded activated

carbon using iron oxide-based nanoparticles Water Res 42, 163–168

Baldrian, P., Merhautová, V., Gabriel, J., Nerud, F., Stopka, P., Hrubý, M., Benes, M.J., 2006

Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous

catalysis by mixed iron oxides Appl Catal B: Environ 66, 258–264

Balmer, M.E., Sulzberger, B., 1999 Atrazine degradation in irradiated iron/oxalate

systems: effects of pH and oxalate Environ Sci Technol 33, 2418–2424

Barrault, J., Abdellaoui, M., Bouchoule, C., Majesté, A., Tatibouët, J.M., Louloudi, A.,

Papayannakos, N., Gangas, N.H., 2000a Catalytic wet peroxide oxidation over

mixed (Al–Fe) pillared clays Appl Catal B: Environ 27, L225–L230

Barrault, J., Bouchoule, C., Echachoui, K., Frini-Srasra, N., Trabelsi, M., Bergaya, F., 1998

Catalytic wet peroxide oxidation (CWPO) of phenol over mixed (AlCu)-pillared

clays Appl Catal B: Environ 15, 269–274

Barrault, J., Tatibouët, J.M., Papayannakos, N., 2000b Catalytic wet peroxide oxidation of

phenol over pillared clays containing iron or copper species C.R Acad Sci Paris,

Sér II C, Chem 3, 777–783

Barreiro, J.C., Capelato, M.D., Martin-Neto, L., Hansen, H.C.B., 2007 Oxidative

decomposition of atrazine by a Fenton-like reaction in a H2O2/ferrihydrite system

Water Res 41, 55–62

Barros, A.L., Pizzolato, T.M., Carissimi, E., Schneider, I.A.H., 2006 Decolorizing dye

wastewater from the agate industry with Fenton oxidation process Miner Eng 19,

87–90

Bell, A.T., 2003 The impact of nanoscience on heterogeneous catalysis Science 299,

1688–1691

Bergaya, F., Aouad, A., Mandalia, T., 2006 Pillared clays and clay minerals In: Bergaya,

F., Theng, B.K.G., Lagaly, G (Eds.), Handbook of Clay Science Elsevier, Amsterdam,

pp 393–421

Bobu, M., Yediler, A., Siminiceanu, I., Schulte-Hostede, S., 2008 Degradation studies of

ciproﬂoxacin on a pillared iron catalyst Appl Catal B: Environ 83, 15–23

Bokare, A.D., Chikate, R.C., Rode, V., Paknikar, M., 2008 Iron–nickel bimetallic

nanoparticles for reductive degradation of azo dye Orange G in aqueous solution

Appl Catal B: Environ 79, 270–278

Brigatti, M.F., Galan, F., Theng, B.K.G., 2006 Structures and mineralogy of clay minerals

In: Bergaya, F., Theng, B.K.G., Lagaly, G (Eds.), Handbook of Clay Science Elsevier,

Amsterdam, pp 19–86

Calabi Floody, M., Theng, B.K.G., Reyes, P., Mora, M.L., 2009 Natural nanoclays:

applications and future trends— a Chilean perspective Clay Miner 44, 161–176

Carriazo, J., Guélou, E., Barrault, J., Tatibouët, J.M., Molina, R., Moreno, S., 2005a

Synthesis of pillared clays containing Al Al–Fe or Al–Ce–Fe from a bentonite:

characterization and catalytic activity Catal Today 107–108, 126–132

Carriazo, J., Guélou, E., Barrault, J., Tatibouët, J.M., Molina, R., Moreno, S., 2005b Catalytic

wet peroxide oxidation of phenol by pillared clays containing Al–Ce–Fe Water Res

39, 3891–3899

Carriazo, J.G., Guelou, E., Barrault, J., Tatibouët, J.M., Moreno, S., 2003 Catalytic wet peroxide

oxidation of phenol over Al–Cu or Al–Fe modiﬁed clays Appl Clay Sci 22, 303–308

Catrinescu, C., Teodosiu, M., Macoveanu, M., Miehe-Brendlé, J., Le Dred, R., 2003

Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite

Water Res 37, 1154–1160

Caudo, S., Centi, G., Genovese, C., Perathoner, S., 2007 Copper- and iron-pillared clay

catalysts for the WHPCO of model and real wastewater streams from olive oil

milling production Appl Catal B: Environ 70, 437–446

Caudo, S., Centi, G., Genovese, C., Perathoner, S., 2008 Copper-pillared clays (Cu-PILC)

for agro-food wastewater puriﬁcation with H2O2 Micropor Mesopor Mater 107,

46–57

Cea, M., 2006 Mecanismosﬁsicoquímicos involucrados en la retención de compuestos

organoclorados en un suelo alofánico Doctor en Ciencias de Recursos Naturales,

Universidad de La Frontera, Chile

Centi, G., Perathoner, S., Torre, T., Verduna, M.G., 2000 Catalytic wet oxidation with H2O2

of carboxylic acids on homogeneous and heterogeneous Fenton-type catalysts

Catal Today 55, 61–69

Chan, K.H., Chu, W., 2005 Model applications and mechanism study on the degradation

of atrazine by Fenton's system J Hazard Mater 118, 227–237

Chen, A., Ma, X., Sun, H., 2008 Decolorization of KN-R catalyzed by Fe-containing Y and ZSM-5 zeolites J Hazard Mater 156, 568–575

Chen, J., Zhu, L., 2006 Catalytic degradation of Orange II by UV-Fenton with hydroxyl-Fe-pillared bentonite in water Chemosphere 65, 1249–1255

Chen, J., Zhu, L., 2007 Heterogeneous UV-Fenton catalytic degradation of dyestuff in water with hydroxyl-Fe pillared bentonite Catal Today 146, 463–470

Cheng, M., Ma, W., Li, J., Huang, Y., Zhao, J., Wen, Y., Xu, Y., 2004 Visible-light-assisted degradation of dye pollutants over Fe(III)-loaded resin in the presence of H2O2at neutral pH values Environ Sci Technol 38, 1569–1575

Cheng, M., Song, W., Ma, W., Chen, C., Zhao, J., Lin, J., Zhu, H., 2008 Catalytic activity of iron species in layered clays for photodegradation of organic dyes under visible irradiation Appl Catal B: Environ 77, 355–363

Childs, C.W., Johnston, J.H., 1980 Mössbauer spectra of proto-ferrihydrite at 77 K and

295 K, and a reappraisal of the possible presence of akaganéite in New Zealand soils Aust J Soil Res 18, 245–250

Chirchi, L., Ghorbel, A., 2002 Use of various Fe-modiﬁed montmorillonite samples for 4-nitrophenol degradation by H2O2 Appl Clay Sci 21, 271–276

Chou, S., Huang, C., 1999 Application of a supported iron oxyhydroxide catalyst in oxidation of benzoic acid by hydrogen peroxide Chemosphere 38, 2719–2731

De León, M.A., Castiglioni, J., Bussi, J., Sergio, M., 2008 Catalytic activity of an iron-pillared montmorillonitic clay mineral in heterogeneous photo-Fenton process Catal Today 133–135, 600–605

Deng, Y., 2007 Physical and oxidative removal of organics during Fenton treatment of mature municipal landﬁll leachate J Hazard Mater 146, 334–340

Deng, Y., Englehardt, J.D., 2006 Treatment of landﬁll leachate by the Fenton process Water Res 40, 3683–3694

Dhakshinamoorthy, A., Pitchumani, K., 2008 Clay entrapped nickel nanoparticles as efﬁcient and recyclable catalysts for hydrogenation of oleﬁns Tetrahedron Lett 49, 1818–1823

Díaz, P., Galindo, G., Escudey, M., 1990 Sintesis de aluminosilicatos semejantes a los existentes en suelos volcanicos Bol Soc Chil Quim 35, 385–389

Diez, M.C., Mora, M.L., Videla, S., 1999 Adsorption of phenolic compounds and color from bleached kraft mill efﬂuent using allophanic compounds Water Res 33, 125–130

Diez, M.C., Quiroz, A., Ureta-Zañartu, S., Vidal, G., Mora, M.L., Gallardo, F., Navia, R., 2005 Soil retention capacity of phenols from biologically pre-treated kraft mill wastewater Water Air Soil Pollut 163, 325–339

Doocey, D.J., Sharratt, P.N., Cundy, C.S., Plaisted, R.J., 2004 Zeolite-mediated advanced oxidation of model chlorinated phenolic aqueous waste part 2: solid phase catalysis Process Saf Environ Prot 82, 359–364

Du, Z., Feng, C., Li, Q., Zhao, Y., Tai, X., 2008 Photodegradation of NPE-10 surfactant by Au-doped nano-TiO2 Colloids Surf A Physicochem Eng Asp 315, 254–258 El-Hamshary, H., El-Sigeny, S., Abou Taleb, M.F., El-Kelesh, N.A., 2007 Removal of phenolic compounds using (2-hydroxyethyl methacrylate/acrylamidopyridine) hydrogel prepared by gamma radiation Sep Purif Technol 57, 329–337 Farjerwerg, K., Castan, T., Foussard, J.-N., Perrard, A., Debellefontaine, H., 2000 Dependency on some operating parameters during wet oxidation of phenol by hydrogen peroxide with Fe-ZSM-5 zeolite Environ Technol 21, 337–344 Farjerwerg, K., Debellefontaine, H., 1996 Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst Appl Catal

B Environ 10, L229–L235

Farjerwerg, K., Foussard, J.-N., Perrard, A., Debellefontaine, H., 1997 Wet oxidation of phenol by hydrogen peroxide: the key role of pH on the catalytic behaviour of Fe-ZSM-5 Water Sci Technol 35, 103–110

Farré, M.J., Doménech, X., Peral, J., 2007 Combined photo-Fenton and biological treatment for Diuron and Linuron removal from water containing humic acid

J Hazard Mater 147, 167–174

Feng, J., Hu, X., Yue, P.L., Zhu, H.Y., Lu, G.Q., 2003a Degradation of azo-dye Orange II by a photoassisted Fenton reaction using a novel composite of iron oxide and silicate nanoparticles as a catalyst Ind Eng Chem Res 42, 2058–2066

Feng, J., Hu, X., Yue, P.L., Zhu, H.Y., Lu, G.Q., 2003b A novel clay-based Fe-nanocomposite and its photo-catalytic activity in photo-assisted degradation of Orange II Chem Eng Sci 58, 679–685

Feng, J., Hu, X., Yue, P.L., 2004a Novel bentonite clay-based Fe-nanocomposite as a heterogeneous catalyst for photo-Fenton discoloration and mineralization of Orange II Environ Sci Technol 38, 269–275

Feng, J., Hu, X., Yue, P.L., 2004b Discoloration and mineralization of Orange II using different heterogeneous catalysts containing Fe: a comparative study Environ Sci Technol 38, 5773–5778

Feng, J., Hu, X., Yue, P.L., 2006 Effect of initial solution pH on the degradation of Orange

II using clay-based Fe nanocomposites as heterogeneous photo-Fenton catalyst Water Res 40, 641–646

Feng, J., Hu, X., Yue, P.L., Qiao, S., 2009 Photo-Fenton degradation of high concentration Orange II (2 mM) using catalysts containing Fe: a comparative study Sep Purif Technol 67, 213–217

Feng, J., Wong, R.S.K., Hu, X., Yue, P.L., 2004c Discoloration and mineralization of Orange II by using Fe3+

-doped TiO2and bentonite clay-based Fe nanocatalysts Catal Today 98, 441–446

Fenton, H.J.H., 1894 Oxidation of tartaric acid in the presence of iron Chem Soc J Lond

65, 899–910

Fernandez, J., Bandara, J., Lopez, A., Albers, P., Kiwi, J., 1998 Efﬁcient photo-assisted Fenton catalysis mediated by Fe ions on Naﬁon membranes active in the abatement

of non-biodegradable azo-dye Chem Commun 1493–1494

Fernandez, J., Bandara, J., Lopez, A., Buffet, Ph., Kiwi, J., 1999 Photoassisted Fenton degradation of nonbiodegradable azo dye (Orange II) in Fe-free solution mediated

by cation transfer membranes Langmuir 15, 185–192

Trang 10

Ferrarese, E., Andreottola, G., Oprea, I.A., 2008 Remediation of PAH-contaminated

sediments by chemical oxidation J Hazard Mater 152, 128–139

Flores, Y., Flores, R., Gallegos, A.A., 2008 Heterogeneous catalysis in the Fenton-type

system reactive black 5/H2O2 J Mol Catal A 281, 184–191

Galindo, G., 1974 Electric charges, sorption of phosphate and cation exchange

equilibria in Chilean Dystrandepts Ph.D Thesis, University of California Riverside

Gallard, H., De Laat, J., 2000 Kinetic modelling of Fe(III)/H2O2oxidation reactions in

dilute aqueous solution using atrazine as a model organic compound Water Res

34, 3107–3116

Georgi, A., Kopinke, F.-D., 2005 Interaction of adsorption and catalytic reactions in

water decontamination processes part I Oxidation of organic contaminants with

hydrogen peroxide catalyzed by activated carbon Appl Catal B Environ 58, 9–18

Giordano, G., Perathoner, S., Centi, G., De Rosa, S., Granato, T., Katovic, A., Siciliano, A.,

Tagarelli, A., Tripicchio, F., 2007 Wet hydrogen peroxide catalytic oxidation of olive

oil mill wastewaters using Cu-zeolite and Cu-pillared clay catalysts Catal Today

124, 240–246

Guélou, E., Barrault, J., Fournier, J., Tatibouët, J.-M., 2003 Active iron species in the

catalytic wet peroxide oxidation of phenol over pillared clays containing iron Appl

Catal B Environ 44, 1–8

Gumy, D., Fernández-Ibáñez, P., Malato, S., Pulgarin, C., Enea, O., Kiwi, J., 2005

Supported Fe/C and Fe/Naﬁon/C catalysts for the photo-Fenton degradation of

Orange II under solar irradiation Catal Today 101, 375–382

Halász, J., Hegedüs, M., Kun, É., Méhn, D., Kiricsi, I., 1999 Destruction of chlorobenzenes

by catalytic oxidation over transition metal containing ZSM-5 and Y (FAU) zeolites

Stud Surf Sci Catal 125, 793–800

Hall, P.L., Churchman, G.J., Theng, B.K.G., 1985 Size distribution of allophone unit

particles in aqueous suspensions Clays Clay Miner 33, 345–349

Hanna, K., Kone, T., Medjahdi, G., 2008 Synthesis of the mixed oxides of iron and quartz

and their catalytic activities for the Fenton-like oxidation Catal Commun 9, 955–959

Henmi, T., Wada, K., 1976 Morphology and composition of allophane Am Mineral 61,

379–390

Huang, H.-H., Lu, M.-C., Chen, J.-N., 2001 Catalytic decomposition of hydrogen peroxide

and 2-chlorophenol with iron oxides Water Res 35, 2291–2299

Huu Phu, N., Kim Hoa, T.T., Van Tan, N., Vinh Thang, H., Le Ha, P., 2001 Characterization

and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous

solutions Appl Catal B Environ 4, 267–275

Iurascu, B., Siminiceanu, I., Vione, D., Vicente, M.A., Gil, A., 2009 Phenol degradation in

water through a heterogeneous photo-Fenton process catalyzed by Fe-treated

laponite Water Res 43, 1313–1322

Jara, A.A., Goldberg, S., Mora, M.L., 2005 Studies of the surface charge of amorphous

aluminosilicates using surface complexation models J Colloid Interface Sci 292,

160–170

Joo, S.H., Zhao, D., 2008 Destruction of lindane and atrazine using stabilized iron

nanoparticles under aerobic and anaerobic conditions: effects of catalyst and

stabilizer Chemosphere 70, 418–425

Kanel, S.R., Neppolian, B., Jung, H., Choi, H., 2004 Comparative removal of polycyclic

aromatic hydrocarbons using iron oxide and hydrogen peroxide in soil slurries

Environ Eng Sci 21, 741–751

Kasiri, M.B., Aleboyeh, H., Aleboyeh, A., 2008 Degradation of Acid Blue 74 using

Fe-ZSM5 zeolite as a heterogeneous photo-Fenton catalyst Appl Catal B Environ 84,

9–15

Kitis, M., Kaplan, S.S., 2007 Advanced oxidation of natural organic matter using

hydrogen peroxide and iron-coated pumice particles Chemosphere 68, 1846–1853

Kloprogge, J.T., 1998 Synthesis of smectites and porous pillared clay catalysts: a review

J Porous Mater 5, 5–41

Kong, S.-H., Watts, R.J., Choi, J.-H., 1998 Treatment of petroleum-contaminated soils

using iron mineral catalyzed hydrogen peroxide Chemosphere 37, 1473–1482

Kurt, U., Apaydin, O., Gonullu, M.T., 2007 Reduction of COD in wastewater from an

organized tannery industrial region by electro-Fenton process J Hazard Mater

143, 33–40

Kušić, H., Koprivanac, N., Selanec, I., 2006 Fe-exchanged zeolite as the effective

heterogeneous Fenton-type catalyst for the organic pollutant minimization: UV

irradiation assistance Chemosphere 65, 65–73

Kuznestsova, E.V.P., Vanina, M.P., Preis, S., 2008 The activation of heterogeneous

Fenton-type catalyst Fe-MFI Catal Commun 9, 381–385

Kwan, W.P., Voelker, B.M., 2002 Decomposition of hydrogen peroxide and organic

compounds in the presence of dissolved iron and ferrihydrite Environ Sci Technol

36, 1467–1476

Kwan, W.P., Voelker, B.M., 2003 Rates of hydroxyl radical generation and organic

compound oxidation in mineral-catalyzed Fenton-like systems Environ Sci

Technol 37, 1150–1158

Kwan, W.P., Voelker, B.M., 2004 Inﬂuence of electrostatics on the oxidation rates of

organic compounds in heterogeneous Fenton systems Environ Sci Technol 38,

3425–3431

Kwon, S.C., Fan, M., Wheelock, T.D., Saha, B., 2007 Nano- and micro-iron oxide catalysts

for controlling the emission of carbon monoxide and methane Sep Purif Technol

58, 40–48

Larachi, F., Lévesque, S., Sayari, A., 1998 Wet oxidation of acetic acid by H2O2catalyzed by

transition metal-exchanged NaY zeolites J Chem Technol Biotechnol 73, 127–130

Lee, B.D., Iso, M., Hosomo, M., 2001 Prediction of Fenton oxidation positions in

polycyclic aromatic hydrocarbons by Frontier electron density Chemosphere 42,

431–435

Li, Y., Lu, Y., Zhu, X., 2006 Photo-Fenton discoloration of the azo dye X-3B over pillared

bentonites containing iron J Hazard Mater 132, 196–201

Lee, C., Yoon, J., 2004 Temperature dependence of hydroxyl radical formation in the hν/

Fe3+/H2O2and Fe3+/H2O2systems Chemosphere 56, 923–924

Li, Y.C., Bachas, L.G., Bhattacharyya, D., 2007 Selected chloro-organic detoxiﬁcations by polychelate (poly(acrylic acid)) and citrate-based Fenton reaction at neutral pH environment Ind Eng Chem Res 46, 7984–7992

Lin, S.-S., Gurol, M.D., 1998 Catalytic decomposition of hydrogen peroxide on iron oxide: kinetics, mechanism, and implications Environ Sci Technol 32, 1417–1423 Lines, M.G., 2008 Nanomaterials for practical functional uses J Alloys Compd 449, 242–245

Liou, M.-J., Lu, M.-C., 2008 Catalytic degradation of explosives with goethite and hydrogen peroxide J Hazard Mater 151, 540–546

Liou, R.-M., Chen, S.-H., Hung, M.-Y., Hsu, C.-S., Lai, J.-Y., 2005 Fe (III) supported on resin

as effective catalyst for the heterogeneous oxidation of phenol in aqueous solution Chemosphere 59, 117–125

Liu, W.-T., 2006 Nanoparticles and their biological and environmental applications

J Biosci Bioeng 102, 1–7

Lu, F., Liu, J., Xu, J., 2008 Synthesis of chain-like Ru nanoparticle arrays and its catalytic activity for hydrogenation of phenol in aqueous media Mater Chem Phys 108, 369–374

Lu, M.-C., Chen, J.-N., Huang, H.-H., 2002 Role of goethite dissolution in the oxidation of 2-chlorophenol with hydrogen peroxide Chemosphere 46, 131–136

Mahmoodi, N.M., Arami, M., Limaee, N.Y., Gharanjig, K., Nourmohammadian, F., 2007 Nanophotocatalysis using immobilized titanium dioxide nanoparticle: degradation and mineralization of water containing organic pollutant: case study of Butachlor Mater Res Bull 42, 797–806

Makhotkina, O.A., Kuznetsova, E.V., Preis, S.V., 2006 Catalytic detoxiﬁcation of 1, 1-dimethylhydrazine aqueous solutions in heterogeneous Fenton system Appl Catal B: Environ 68, 85–91

Malato, S., Blanco, J., Maldonado, M.I., Oller, I., Gernjak, W., Pérez-Estrada, L., 2007 Coupling solar photo-Fenton and biotreatment at industrial scale: main results of a demonstration plant J Hazard Mater 146, 440–446

Mamalis, A.G., 2007 Recent advances in nanotechnology J Mater Process Technol

181, 52–58

Martínez, F., Calleja, G., Melero, J.A., Molina, R., 2007 Iron species incorporated over different silica supports for the heterogeneous photo-Fenton oxidation of phenol Appl Catal B Environ 70, 452–460

Matta, R., Hanna, K., Chiron, S., 2007 Fenton-like oxidation of 2, 4, 6-trinitrotoluene using different iron minerals Sci Total Environ 385, 242–251

Mecozzi, R., Di Palma, L., De Filippis, P., 2008 Effect of modiﬁed Fenton treatment on the thermal behavior of contaminated harbor sediments Chemosphere 71, 843–852 Mishra, T., Parida, K.M., Rao, S.B., 1996 Transition metal oxide pillared clay: 1 A comparative study of textural and acidic properties of Fe(III) pillared montmoril-lonite and pillared acid activated montmorilmontmoril-lonite J Colloid Interface Sci 183, 176–183

Mishra, T., Mohapatra, P., Parida, K.M., 2008 Synthesis, characterisation and catalytic evaluation of iron-manganese mixed oxide pillared clay for VOC decomposition reaction Appl Catal B Environ 79, 279–285

Miyazaki, K., Islam, N., 2007 Nanotechnology systems of innovation— an analysis of industry and academia research activities Technovation 27, 661–675

Montarges-Pelletier, E., Bogenez, S., Pelletier, M., Razaﬁtianamaharavo, A., Ghanbaja, J., Lartiges, B., Michot, L., 2005 Synthetic allophane-like particles: textural properties Colloids Surf., A Physicochem Eng Asp 255, 1–10

Mora, M.L., Escudey, M., Galindo, G., 1994 Sintesis y caracterización de suelos alofanicos Bol Soc Chil.Quim 39, 237–243

Mora, M.L., 1992 Sintesis, caracterización y reactividad de un suelo alofanico modelo Universidad de Santiago de Chile, Departamento de Química

Muthuvel, I., Swaminathan, M., 2008 Highly solar active Fe(III) immobilised alumina for the degradation of Acid Violet 7 Sol Energy Mater Sol Cells 92, 857–863 Navia, R., Fuentes, B., Lorber, K.E., Mora, M.L., Diez, M.C., 2005 In-series columns adsorption performance of Kraft mill wastewater pollutants onto volcanic soil Chemosphere 60, 870–878

Navia, R., Levet, L., Mora, M.L., Vidal, G., Diez, M.C., 2003 Allophanic soil adsorption system as a bleached kraft mill aerobic efﬂuent post-treatment Water Air Soil Pollut 148, 323–333

Neamtu, M., Catrinescu, C., Kettrup, A., 2004a Effect of dealumination of iron(III)-exchanged Y zeolites on oxidation of Reactive Yellow 84 azo dye in the presence of hydrogen peroxide Appl Catal B Environ 51, 149–157

Neamtu, M., Zaharia, C., Catrinescu, C., Yediler, A., Macoveanu, M., Kettrup, A., 2004b Fe-exchanged Y zeolite as catalyst for wet peroxide oxidation of reactive azo dye Procion Marine H-EXL Appl Catal B Environ 48, 287–294

Nogueira, R.F.P., Trovó, A.G., da Silva, M.R.A., Villa, R.D., de Oliveira, M.C., 2007 Fundamentos e aplicações ambientais dos processos Fenton e foto-Fenton Quim Nova 30, 400–408

Noorjahan, M., Kumari, V.D., Subrahmanyam, M., Panda, L., 2005 Immobilized Fe(III)-HY:

an efﬁcient and stable photo-Fenton catalyst Appl Catal B Environ 57, 291–298 Núñez, L., García-Hortal, J.A., Torrades, F., 2007 Study of kinetic parameters related to the decolourization and mineralization of reactive dyes from textile dyeing using Fenton and photo-Fenton processes Dyes Pigm 75, 647–652

Nurmi, J., Tratnyek, P.G., Sarathy, V., Baer, D.R., Amonette, J.E., Pecher, K., Wang, C., Linehan, J.C., Matson, D.W., Penn, R.L., Driessen, M.D., 2005 Characterization and properties of metallic iron nanoparticle: spectroscopy, electrochemistry, and kinetics Environ Sci Technol 39, 1221–1230

Nutt, M.O., Heck, K.N., Alvarez, P., Wong, M.S., 2006 Improved Pd-on-Au bimetallic nanoparticle catalysts for aqueous-phase trichloroethene hydrodechlorination Appl Catal B Environ 69, 115–125

Ohashi, F., Wada, S.-I., Suzuki, M., Maeda, M., Tomura, S., 2002 Synthetic allophane from high-concentration solutions: nanoengineering of the porous solid Clay Miner 37, 451–456

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